. another to the president of the united states. for an hour and a half this morning alerts were sounded on capitol hill. >> close the other side of the street. we are closing off the sidewalk. >> reporter: some senate offices were cleared. staff in others were told to stay inside. after two letters -- one to mississippi republican senator roger wicker, the second to president obama -- tested preliminarily for ricin. both were quarantined at a post office screening facility miles away in maryland. built after the anthrax attacks that killed five and injured 17 across the nation in 2001. >> the president -- i'm sure you will ask this. the president has, of course, been briefed on these letters. he was briefed last night and again this morning. >> reporter: the fbi said both were postmarked memphis, tennessee, on april 8. they used the same language. quote, to see a wrong and not expose it is to become a silent partner to its continuance. a phrase often used by radical groups. both letters are signed, i am kc and i approve this message. a third letter went to democratic senator carl levin'